In mobile communication systems such as LTE, it is common that a user apparatus UE and a base station eNB perform communication so that communication is performed between user apparatuses UE via the base station eNB and the like. However, in recent years, various techniques are proposed on D2D communication (to be referred to as D2D hereinafter) for performing direct communication between user apparatuses UE.
Especially, in D2D of LTE, there are proposed “Communication” for performing data communication such as push telephone call and the like between user apparatuses UE, and “Discovery” in which a user apparatus UE transmits a discovery message including an application ID and the like so as to cause a user apparatus UE of a receiving side to detect the user apparatus UE of the transmitting side (refer to non-patent document 1, for example).
In the D2D specified in LTE, each user apparatus UE uses a part of uplink resources already specified as transmission resources of an uplink signal from the user apparatus UE to the base station eNB. In the following, outline of signal transmission of D2D in LTE is described.
As to “Discovery”, as shown in FIG. 1A, a resource pool for Discovery message is kept for each Discovery period, so that the user apparatus UE transmits a Discovery message in the resource pool. More particularly, there are Type1 and Type2b. In Type1, the user apparatus UE autonomously selects a transmission resource from the resource pool. In Type2b, a semi-static resource is assigned by an upper layer signaling (RRC signal, for example).
Also, as to “Communication”, as shown in FIG. 1B, a resource pool for Control/Data transmission is periodically kept. A user apparatus in the transmission side notifies the reception side of resources for Data transmission and the like by SCI (Sidelink Control Information) using a resource selected from the Control resource pool, and transmits Data using a resource for Data transmission. As to “Communication”, more particularly, there are Mode1 and Mode2. In Mode1, a resource is dynamically assigned by a (E)PDCCH transmitted from the base station eNB to the user apparatus UE. In Mode2, the user apparatus UE autonomously selects a transmission resource from a resource pool for Control/Data transmission. As to the resource pool, it may be notified by a SIB, or a pre-defined one is used.
In LTE, a channel used for “Discovery” is referred to as PSDCH (Physical Sidelink Discovery Channel), a channel for transmitting control information such as SCI in “Communication” is referred to as PSCCH (Physical Sidelink Control Channel), and a channel for transmitting data is referred to as PSSCH (Physical Sidelink Shared Channel) (non-patent document 2).